S6 Engine Issue

I need some help.

About two years ago, I purchased a 2014 S6. Over the past year, it has been in the shop multiple times. First, the engine developed that whistle and the dealer covered the expense. Then my turbos failed. I thought it was due to some bad gas because I had just filled up about a mile before the car started smoking and idling rough. I had it towed to the dealer and asked them to check the fuel, but they didn’t. They determined the turbos were the problem and replaced both turbos. About two weeks later, my car started to idle rough and stalled. I had it towed back to the dealer to discover that there was what seemed to be water in the fuel. The dealer drained the fuel and replaced the fuel filter. About two weeks later, the car shut off while I was driving. I had it towed to a different dealer and they diagnosed that the starter had failed. They replaced the starter to discover that the engine would still not turn over. Now they say the engine needs to be replaced because they found metal shavings in the oil.

Any thoughts on what could have caused this?